Temperature effects on egg and larval development rate in European smelt,Osmerus eperlanus,experiments and a 50 year hindcast

This study investigates the effect of water temperature on the development rate of eggs and larvae, the duration of the endogenous feeding period and its consequences for recruitment of smelt (Osmerus eperlanus) in Dutch lakes IJsselmeer and Markermeer. This study measured temperature-dependent egg and larval development rates as well as mortality rates from fertilization till the moment of absorption of the yolk-sac and from yolk-sac depletion onwards in temperature-controlled indoor experiments. Using multinomial modelling the authors found significant differences in development time of egg development stages under different temperature regimes. Based on historic water temperatures, the model predicted that the larval endogenous feeding period has advanced at a rate of about 2.9 days per decade in a more than 50 year period since 1961, yet there was no change in the duration of the endogenous feeding period. As zooplankton is more responsive to daylight than water temperature cues, a mismatch between the peak of the onset of exogenous feeding of smelt and the peak of zooplankton blooms could lead to high mortality and therefore low recruitment of smelt. Such a mismatch might contribute to a decline in the smelt population in Lake IJsselmeer and Lake Markermeer.     

Interactive community responses to disturbance in streams: disturbance history moderates the influence of disturbance types

Both disturbance history and disturbance type act to structure communities through selecting for particular species traits but they may also interact. For example, flooding selects for species with flood‐resistant traits in streams, but those traits could make communities susceptible to other disturbances and so could cause shifts in community composition due to anthropogenic climate change. To better understand the interactive influences of disturbance history and type on community composition, we investigated the response of macroinvertebrate communities to disturbance using in‐stream channels. Using a split‐plot design, individual channels in five ‘stable’ streams and five ‘frequently disturbed’ streams (disturbance history) were subject to different disturbance type treatments (flooding, drying and a control). Disturbance type independently drove effects on species diversity, but all other effects of disturbance type depended on disturbance history. In particular, the interaction of disturbance type and history determined overall community response. Both disturbance types tested produced similar community responses in frequently disturbed streams, including changes in community composition and alterations to the abundance of less mobile taxa, but low‐flow had a significantly greater effect in stable streams. Macroinvertebrate drift was greatest in the rock‐rolling treatments and significantly less in the low‐flow treatment for both disturbance histories. Therefore, disturbance history moderated the effects of disturbance type and determined the mechanism of community response by determining how well species were adapted to disturbance. This outcome suggests that previous disturbances strongly influence how vulnerable communities are to changes in disturbance, and so should be considered when predicting how changes in disturbance regimes will affect future community composition.     

The importance of ecotype diversity on duckweed growth with and without salt stress

生态型多样性对存在盐分胁迫和不存在盐分胁迫下浮萍生长的重要性 淡水生态系统受到的污染正在威胁着全世界淡水植物物种的多样性。浮萍(Lemna minor)等淡水植物对新出现的逆境条件具有潜在的敏感性。为了测试生态型的多样性是否可以增强这类植物对逆境的抗性，本研究使用了7个浮萍种群，并沿着一个生态型多样性梯度对存在和不存在中度盐分胁迫时的种群生长速率进行了测量。这些浮萍种群在92个实验围隔中生长了5个月，其中有生态型单一栽培，也有在5或3个同种生态型(23种独特组合)中混合栽培。在无扰条件下生长一段时间(阶段1)后，这些浮萍栽培物将被置于中等盐分胁迫(50 mmol/L NaCl)条件下数周时间(阶段2)。实验进行时存在着与不同生态型伴生的天然表观微生物群落(epimicrobial community)。在阶段2中，这些藻类的一部分受到了随机二次胁迫。这些生态型表现出了不同的生长速率，其中最快的生长速率是其它生态型的两倍。多样性的环境进一步影响了生态型的生长速率，生态型混合栽培的植株在实验结束时具有更高的丰度，因此，随着时间的推移，环境逐渐恶化，生态型的多样性也将变得更为重要。上述研究结果表明，种内生长速率的差异体现了生态型多样性对种群丰度的正向影响。在中等盐度水平下的暴露并未显著影响浮萍的生长速率，尽管这种效应可能被盐性环境中更小的藻类压力所掩盖。     

A combined numerical and experimental technique for estimation of the forces and moments in the lumbar intervertebral disc

Evaluation of the loads on lumbar intervertebral discs (IVD) is critically important since it is closely related to spine biomechanics, pathology and prosthesis design. Non-invasive estimation of the loads in the discs remains a challenge. In this study, we proposed a new technique to estimate in vivo loads in the IVD using a subject-specific finite element (FE) model of the disc and the kinematics of the disc endplates as input boundary conditions. The technique was validated by comparing the forces and moments in the discs calculated from the FE analyses to the in vitro experiment measurements of three corresponding lumbar discs. The results showed that the forces and moments could be estimated within an average error of 20%. Therefore, this technique can be a promising tool for non-invasive estimation of the loads in the discs and may be extended to be used on living subjects.     

The Role of Natural Enemies in the Germination and Establishment of Pachira (Malvaceae) Trees in the Peruvian Amazon

Seeds from Pachira brevipes from white‐sand forest and Pachira insignis from clay forest were placed in a reciprocal transplant experiment that manipulated herbivore presence. Pachira insignis experienced 80 percent leaf loss in both habitats from herbivores, causing 79 percent mortality in white‐sand compared with 47 percent in clay in just 3 mo. Pachira brevipes suffered pathogen attack in both habitats that killed 90 percent of its establishing seedlings. Natural enemies thus strongly influence seedling recruitment of these two Pachira species in these forests and appear to have the largest impact within the seedlings' first few months.     

Recolonization of infauna on a tidal flat: An experimental analysis of modes of dispersal

Animals can colonize intertidal sediments by lateral movement through (by burrowing) and on (by crawling) the sediment or by settling (vertically) from the water-column (during larval or bed-load transport above the surface of the sediment). To determine the relative importance of these in recolonization of cleared areas, animals were experimentally prevented from lateral movement through sediments (using fences) and/or by settlement from the water-column (using lids). Necessary controls required nine experimental treatments and an untouched control. After 16 days, assemblages in experimental treatments differed from natural assemblages: recovery was not yet complete. There were differences among assemblages in plots with lids, but no differences among assemblages in plots with fences. After 33 days, treatments with lids still showed little recolonization. Multivariate analyses of assemblage showed the relevance of colonization from the water-column. Analysis of individual taxa revealed complex patterns of recolonization. In general, juvenile bivalves used the water-column, but numbers of large polychaetes were reduced by the fences, indicating that lateral movement was important. These experiments illustrate the complex dynamics of soft-bottom benthic assemblages and great importance of small-scale dispersal.     

In Vivo Accumulation of Plastic-Derived Chemicals into Seabird Tissues

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